Conventionally, a packet data unit (PDU) session involves managing a data routing path between a UE and a Data Network (DN) in 5G communication system. A UE or a 5GS may utilize a PDU session establishment procedure such as the procedure defined in TS 23.502 to create a PDU session to establish user traffic between a UE and one or more DNs. After establishing a PDU session, a UE may access services provided by the DNs. Specifically, the UE may map user traffic to a suitable Quality of Service (QoS) rule provided by the 5GS to transmit user traffic in the user plane. User Routing Selection Policy (URSP) rules could be provided by a 5GS or could be pre-configured within the UE to guide the UE to establish a data routing path on PDU sessions by using different access networks.
TABLE 1PCFpermittedInformationto modify innameDescriptionCategoryUE contextScopeRuleDetermines theMandatoryYesUE ContextPrecedenceorder the URSPrule is enforcedin the UETrafficDefines trafficdescriptordescriptors ofpolicyApplicationApplicationOptionalidentifiersidentifier(s)IPIP 3 tuple(s)OptionalYesUE ContextdescriptorsNon-IPDescriptor(s) forOptionalYesUE Contextdescriptorsnon-IP trafficRouteThe componentsMandatorySelectionfor Routedescriptorselection (seeTable 6.6.2-2)
Table 1 shows an example of URSP rules provided by a Home Public Land Mobile Network (HPLMN) to a UE as defined by Table 6.6.2-1 of TS 23.503. The URSP rules may include (1) rule precedence which determines the order of the URSP rules that are enforced in the UE, (2) traffic descriptor which defines the traffic descriptors for the policy, (3) application identifier which contains an application identifier (ID), (4) IP descriptors which include an destination IP, address or IPv6 network prefix, destination port number, and protocol ID of the protocol above IP,
(5) non-IP descriptors which include a descriptor for non-IP traffic, and (6) route selection descriptor which includes needed components for route selection.
Each URSP rule may contain a route selection descriptor which could be used to determine when a rule is applicable. Table 2 shows an example of Route Selection Descriptor provided by a Home Public Land Mobile Network (HPLMN) to a UE as defined by Table 6.6.2-2 of TS 23.503.
TABLE 2PCFpermittedto modifyInformationUE in UEnameDescriptionCategorycontextScopeRouteDefines routeMandatoryselectionselectioncomponentscomponentsSSC ModeOptionalYesUE ContextSelectionNetworkOptionalYesUE ContextSliceSelectionDNNOptionalYesUE ContextSelectionNon-Indicates if trafficOptionalYesUE Contextseamlessof matchingOffloadapplication to beIndicationoff-loaded to non-3GPP access outsideof PDU sessionAccess typeIndicates theOptionalYesUE Contextprecedencepreferred Accesstype (3 GPP or non-3 GPP) when UEestablishes PDUsession for matchingapplication
An application inside a UE could be analyzed to determine if any URSP is applicable for its data flow. The analyzed information may include (1) selection components, (2) Session and Service Continuity (SSC) mode selection, (3) network slice selection, (4) DNN selection, (5) non-seamless offload indication, and (6) access type. Therefore, UE may use the provisioned URSP rules to configure the data flow and to decide whether the UE would need to create new PDU sessions or use the current existing PDU sessions or release the current PDU sessions or modify the current PDU sessions.
In a 5GS, a UE may create a Multi-Access (MA) PDU session in which user plane traffic can be transmitted between a UE and a DN by using different access network simultaneously. FIG. 1 illustrates a network architecture through which a UE may communicate with a DN by using two different access networks. As illustrated in the FIG. 1, the may UE physically established two PDU sessions with two different access networks which are e.g., next generation radio access network (NG-RAN) and Wi-Fi, but the two PDU sessions are with the same data network. In other words, the UE may physically and independently utilize two different packet data routing paths to exchange the UE's user plane traffic to the same DN. According to URSP rules configured by 5GS, a UE may use stored URSP rules to decide which data packets would belong to which single-access PDU session. The UE may determine whether to use the existing PDU session or to create a PDU session. The stored URSP rules could be updated by the 5GS as needed based on a current 5GS procedure.
Based on the above description, it can be known that a PDU session is only applicable to only one type of access network as currently defined by the 5GS, and a UE may utilize one or more PDU sessions on one type of network and one or more other PDU sessions on another type of access network. However, the UE may not be able to use the PDU sessions efficiently to connect to a specific DN when multiple PDU sessions are created across multiple types of access technologies. For example, referring to FIG. 1, if a UE were to have a new data flow which transmits user plane traffic to a DN, and both existing PDU sessions would be able to satisfy the QoS requirements, then it would be unclear which access network should be used to transmit a data traffic between the UE and the DN.
For another example, if a UE has established an existing PDU session through a NG-RAN to exchange data traffic between the UE and a DN, but later on the UE has detected that the PDU session is better off switched to Wi-Fi which provides a better performance, then it is unclear how the UE would switch the current PDU session to a different session with the Wi-Fi. Also, if this UE has the ability to use both access networks simultaneously, then it is unclear how the UE should split the data traffic between the two access networks in order to communicate with the DN.
Even though the 5G-UE may be able to simultaneously use multiple access networks including a 3GPP network and a Non-3GPP network to establish a multi-access data connection (i.e., MA-PDU Session) with same Data Network (DN), currently there is no established way to establish a MA-PDU Session, and there is no established way for a UE to transmit UL data traffic by steering a data traffic between multiple access networks.